The present invention relates generally to video cassettes and more particularly to editing programs on a video cassette. Recently, the video cassette recorder has become a popular means for recording and viewing video programming. The editing of such programming has always been difficult because video cassette recorders used to record and play back programming do not include an editing device which can make measurements as a function of time. The only measurement device included in most video cassette recorders is a counter which counts up or down for a specific number of turns of a take-up reel of the video cassette recorder. The only way for a user to advance the tape or rewind the tape by a desired time period is to either guess or fast forward the tape while monitoring the TV set in preview mode. These techniques for measuring can be both frustrating and an inconvenience to the user.
Another type of editing device frequently implemented in video cassette recorders is a memory function which gives the video cassette recorder the capability of rewinding to a specific point if the user has indicated that point before recording or playing of the tape begins. The memory function is useful for keeping track of one programming point on the tape. However, it is quite limited as far as its ability to act as an editing device and does not give a user control over relative length of the tape expressed as a function of time.
One problem associated with editing a video cassette with regard to time functions is that the different sections of tape in the cassette are moving at different take-up reel count rates at any point in time. Portions of tape at the end of the reel count much slower than portions at the beginning of the tape. Therefore, devices for editing which detect the number of turns of tape around the reels are inaccurate because these measurements change as the tape moves from one reel to the other. Another problem is that it is difficult to take into account the tightness of the tape around the reels and the thickness of the tape. Measurements of tape length can be skewed due to these factors.